Internal combustion engines are controlled in many different ways to provide acceptable driving comfort during all operating conditions. Some methods use engine output, or torque, control where the actual engine torque is controlled to a desired engine torque through an output adjusting device, such as with an electronic throttle, ignition timing, or various other devices.
It is known that there is the potential for poor driveability when the vehicle operator releases and subsequently engages the accelerator pedal. Specifically, as described in U.S. Pat. No. 6,266,597, this results due to transmission or driveline gear lash. For example, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission or driveline separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, or clunk, resulting in poor driveability and customer dissatisfaction.
This disadvantage of the prior art is exacerbated when the operator returns the accelerator pedal to a depressed position, indicating a desire for increased engine torque. In this situation, the zero torque transition point must again be traversed. However, in this situation, the engine is producing a larger amount of torque than during deceleration because the driver is requesting acceleration. Thus, another, more severe, impact is generally experienced due to the transmission or driveline lash during the zero torque transition.
As such, in U.S. Pat. No. 6,266,597, the system controls engine torque to transition through the transmission or driveline lash zone. The transmission or driveline lash zone is determined using speed ratio across the torque converter. When near the transmission lash zone, engine torque is adjusted at a predetermined rate until the system passes through the transmission lash zone. By limiting the change of torque in this way, driveability is improved and it is possible to quickly and reliably provide negative engine torque for braking.
However, the inventors herein have recognized a disadvantage with such an approach. In particular, not all situations require rate limiting, and in particular, some situations require more or less filtering than others. For example, during some conditions the driver does not feel the transmission clunk as well as during other conditions. Likewise, the driver may rather tolerate some mild transmission or driveline clunk to obtain improved engine response in some situations.